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In order to study the distribution of gas and ionizing radiation around etaCar and their implications for its likely companion star, we have examinedhigh-excitation emission lines of [Ne III], [Fe III], etc., in spectra obtainedwith the HST/STIS instrument during 1998-2004. Our principal results, some ofthem unexpected, are: (1) The high-excitation fluxes varied systematically andnon-trivially throughout eta Car's 5.5-year spectroscopic cycle. Instead ofrising to a plateau after the 1998 "event," they changed continuously with amaximum in mid-cycle. (2) At one significant location a brief, strong secondarymaximum occurred just before the 2003.5 spectroscopic event. (3) These emissionlines are strongly concentrated at the "Weigelt knots" several hundred AUnorthwest of the star. With less certainty, [Ne III] appears to be somewhatmore concentrated than [Fe III]. (4) A faster, blue-shifted component of eachfeature appears concentrated near the star and elongated perpendicular to thesystem's bipolar axis. This structure may be related to the equatorial outflowand/or to dense material known to exist along our line of sight to the star.(5) Using the photoionization program Cloudy, we estimated the range ofparameters for the hot secondary star that would give satisfactoryhigh-excitation line ratios in the ejecta. Teff = 39000 K and L = 4 Lsun,for example, would be satisfactory. The allowed region in parameter space iswider (and mostly less luminous) than some previous authors suggested.

High-excitation emission lines near eta Carinae, and its likely companion star